OLFACTORY ORGANS — EXERCISE ANl) POWER. 
221 ) 
111 addition to the true osphradia, there have been detected in 
certain species not within oiir scope, other sensory organs of probably 
analogous function, which may exist in the Asiphonated species as a 
pair of epithelial papillated sensory areas, iuneiwated from the 
posterior pallial nerve and placed at each side of the anus. 
In the Siphouated forms these organs may exist upon the siphonal 
retractors or at the base of the branchial siiihon in the form of papilhe, 
tentacles, or lamellai, and receive their innervation from a special 
siphonal ganglion. 
Odours of various kinds are undoubtedly attractive to snails and 
slugs, which, in all probability, discriminate their food by the aid of the 
olfactory sense, this faculty in A vion and other genera being effectually 
functional at comparatively gveat distances, even for isolated objects 
of restricted size. IMoij^uin-Tandon has recorded that in the Jardiii des 
Plantes, Toulouse, he observed one rainy day two Liman- maximm 
crawling from different points towards a decaying apple ; he raised the 
fruit and moved it to the right and afterwards to the left of the 
animals, but the Limaces unerringly changed their direction in ac- 
cordance with the altered position of the fruit, never moving in a 
wrong direction. When the fi’uit was held above them the tentacles 
and body were directed towards it and efforts apparently made to 
find some means of reaching the food. 
It has also been well established that snails (quickly emerge from 
their shells when food they like is placed beside them, the odour in 
these cases being the only available indication of its presence, visual 
assistance being impossible. 
Helix aspevsa, as is knovm, will fiequently traverse with much labour 
broad dusty roads and climb rough walls to reach some favourite food, 
this being another evidence of the keenness of the olfactory faculty. 
In the Pelecypoda the evidences of the exercise of this function are 
few. Mr. King has, however, recorded the attraction by putrefying 
flesh of large numbers of Pisidium pusillum, which, in a few days’ 
time, were found clustered upon the skull of a fox placed in a small 
ditch to soak, doubtless feeding upon the minute floating particles of 
flesh and the organisms developed thereon. 
The Exhalation of strong and special odours by the animals of 
certain genera is probably connected with their season of reproduc- 
tion and may possibly be of a signalling character, and though, in 
some cases, doubtless of a protective nature, would seem to imply in 
